Issue
You can read one of the following error messages on your Drupal website
Search API Solr 8.x-1.x is unsupported. Upgrade to 8.x-3.x or newer.or
The support for Search API Solr 8.x-1.x ends 2020-12-31. Ensure to upgrade to 8.x-3.x in combination with the Acquia Search Solr module...Resolution
We recommend that you disregard the message for now, as Acquia will sponsor continued maintenance of the Search API Solr 8.x-1.x module by the Drupal community through December 31, 2020, and there should be no danger or problem whatsoever if you continue to use the above mentioned module versions.